1. Field of the Invention
Aspects of the present invention relate to an optical scanning unit and an electro-photographic image forming apparatus that employs the same.
2. Description of the Related Art
An electro-photographic image forming apparatus includes an optical scanning unit that scans light modulated in response to image information, to a photosensitive body (exposure object), and deflects the light in a main scanning direction using a deflector, such as a polygon mirror. The optical scanning unit includes a collimating lens, a cylindrical lens, and an fθ lens, in order to focus light radiated from a light source, onto a photosensitive body. Refractive indexes of the above lenses vary according to temperature, and such variations may cause focus movement. For example, the light radiated from the light source may not be accurately focused on the photosensitive body. Also, the wavelength of light radiated from the light source varies according to the temperature of the light source. If the wavelength of light varies, the refraction characteristics of the light are also changed. Due to the variations in wavelength of the light, focus movement can also occur. If focus movement occurs, the light may be improperly focused onto a photosensitive body, thereby reducing the quality of printed images formed by the photosensitive body.